Chamber filter presses, filter plate regulating arrangements, membrane plates, and filter guide arrangements have been proposed in, for example, U.S. Pat. No. 4,686,596 and corresponding European patent 0 125 456, as well as in U.S. Pat. Nos. 4,853,121, 4,855,062, and 4,764,273.
Additionally, in German patent 2,933,096, with a membrane plate being a planar membrane fashioned as a rubber cloth and including a relatively soft-elastic material so that the membrane may follow the directions alternatingly caused by the filtration pressure and pressure of the press without the danger of tearing at the clamping rim.
One difficulty in the above proposed membrane plate resides in the fact that, during the deflections, considerable tensile stresses occur within the membrane and, with soft-elastic membranes, such tensile stresses results in the creep of the material in the zone of the clamping rim, which creep is cumulative with each deflection. Consequently, leakages ultimately develop within the region of the clamping rim.
In European patents 70,473 and 125,456, it is also proposed to provide, for the membrane plates, a clearance for movement between the frame and the supporting plates so that the membrane is lifted at the clamping rim with each opening of the filter press, and with the membrane, in each case, being restored with regard to the material creep so that the deleterious cumulative effect of the creep is eliminated.
However, a disadvantage of the last mentioned proposed membrane construction resides in the fact that the soft-elastic membranes are highly susceptible to corrosion when exposed to aggressive media such as, for example, a filtering material that contains sulfuric acid. Thus, with such an arrangement, in industrial applications, the service life of the filter presses is substantially reduced.
While hard-elastic membrane plates of suitable synthetic resin materials may be utilized which are resistant to corrosion a disadvantage of this approach resides in the fact that the hard-elastic membrane plates can only execute a very limited deflection movement. Moreover, there is an additional danger that the hard-elastic membrane plates may tear or rupture along the clamping rim. However, for economical usage of filter presses, it is considerably important to be able to provide a maximally large filter cake space which perforce requires broad deflection paths for the membranes.
In, for example, DOS 2,712,753, filter press membranes are provided which are formed integrally at a relatively thick peripheral frame and are in contact with a supporting plate almost over an entire area thereof on a side of the press medium chamber so that the membrane plates can be deflected substantially only toward one side of the basic position. Consequently, with such an arrangement, only half-size filter cake chambers may be provided or, alternatively, the membrane must be adapted to execute, with the filter cake chamber being the same size, twice as wide a deflection path toward one side. In order to reduce internal tensile stress on the membrane during such deflection, an undulating membrane region is provided, with the region adjoining the frame, and the waves or undulations in the region are flattened upon a deflection of the membrane.
With an undulating membrane, considerable transverse forces occur at the clamping rim at the particularly critical stress exerted by the press medium pressure, since, at this rim, the wave or undulation crest must execute a wide deflection path prior to finding support, if at all, on a compressed filter cake. Moreover, the external undulations or wave crests execute a strong pivotal motion oriented or directed toward the rim so that crease formation can occur in the filter cloth in contact with the wave or undulation crest resulting in a premature wear of the filter cloths.